Instrument panel for air bag

ABSTRACT

In order to reconcile the cleaving performance and the quality of appearance of an instrument panel for an bag, an instrument panel is provided having a skin member of a single layer structure, a cleaving section formed by a groove provided on the back of the skin member is composed of a longitudinal cleaving section which is substantially linear and a pair of &#34;V &#34; shaped lateral cleaving sections which are ramified respectively from both ends of the longitudinal cleaving section and which open forward and extend obliquely with respect to the direction of extension of the longitudinal cleaving section. Furthermore, where a skin member of a double-layered structure in which at least a cushion layer is disposed on the back of a skin layer, a door member is formed on the back of a skin member, in which a brittle section is created, as one body there with by injection-molding a resin material and a brittle section of the door member facing the brittle section of the skin member.

BACKGROUND OF THE INVENTION

The present invention relates to an instrument panel for an air bag,which stores an air bag for a passenger seat in particular among vehicleair bags, in a folded state at the inside thereof and which cleaves soas to deploy the air bag in front of a passenger as the air bag inflatesin emergency.

An air bag system for constraining a passenger by being inflated when avehicle collides is disposed at the inside of an instrument panel inmany recent vehicles.

While a cleaving section for deloying the air bag within the car room isprovided in the instrument panel of this type, the quality of appearanceof the instrument panel is liable to degrade in general when thecleaving performance is to be enhanced. This is because the cleavingsection is created by embrittling the part of the instrument panelcorresponding to an air bag deployment section. Therefore, it isrequired to reconcile and have both the cleaving performance and thequality of appearance of the instrument panel for an air bag.

Some of such instrument panels have a cushion layer made of foam resin.Such instrument panels include (1) one in which a skin member, a doormember and the cushion layer are formed in a body by injecting andfoaming the foam material between the skin member and the door memberhaving a single-layer structure, (2) and another one in which a skinmember having a double-layer structure formed by molding a skin layerand the cushion layer in a body in advance is formed in a body with thedoor member by injection-molding synthetic resin, thus forming the doormember on the back of the skin member. The difference of thosestructures originates mainly from the difference of the foam resinsforming the cushion layer, i.e. polyurethane foam resin is used usuallyfor the former and polyolefine foam resin is used usually for thelatter.

In the panel using the skin member having the single-layer structure,the cleaving section, for example, is created by providing a groove bymeans of a high-frequency welder or the like on the back of the skinmember at the part corresponding to the air bag deployment section.

While a relatively hard type of the vinyl chloride resins has been usedfor such a skin member having the single-layer structure, and thus theabove-mentioned cleavage was relatively readily achieved in the past,some of the skin members are made of soft PVC (poly-vinyl chloride) orTPO (styrene or olefinic thermoplastic elastomer) recently, thus causinga problem that the cleaving section cleaves less readily as compared tothe past ones because such material has extensibility and flexibilitymore than the above-mentioned material.

Further, although the cleavage may be achieved more readily by thinningthe thickness of the cleaving section, there has been a problem that themoldability of the thin part and the durability of the product drop dueto the characteristics of the PVC and TPO, thus damaging the quality ofappearance thereof.

Meanwhile, in the panel using the skin member having the above-mentioneddouble-layer structure, as shown for example in FIG. 14, a cleavingsection 105 is created by molding a door member 104 made ofthermoplastic resin by means of injection molding on the back of and ina body with a skin member 103 formed by disposing a cushion layer 101made of foam resin and a barrier layer 102 made of soft resin on theback of a skin layer 100 and by cutting the part of the door member 104and the skin member 103 corresponding to the air bag develoyment sectioninto the shape as shown in the figure by means of ultrasonic or ahigh-frequency laser.

Because the cleaving section 105 is created after the molding, i.e.after producing the instrument panel, the door member 104 isdisconnected in creating the cleaving section 105. Therefore, there hasbeen a problem that because the rigidity of the part corresponding tothe cleaving section 105 is low during normal use, the skin layer 100 isdented or wrinkled locally, thus damaging the quality of appearance asstress is concentrated on the thin part of the skin member 103 where therigidity is low when force is applied by touching the instrument panelfor example.

Further, it requires a cumbersome post-processing of creating thecleaving section 105 after the production of the instrument panel. Itstill further requires highly advanced technology keeping the depth ofthe cut for creating the cleaving section 105 constant and incontrolling the thickness of the panel at the part corresponding to thecleaving section 105. These have caused an increase in production cost.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to solve theabove-mentioned problems by reconciling cleaving performance duringinflating an air bag and quality of appearance thereof during normal useof an instrument panel with a skin member having a single ordouble-layer structure as described above.

An instrument panel for an air bag of the present invention ischaracterized in that a cleaving section, which cleaves as an air baginflates, is formed by a groove that is created on the back of a skinmember, the cleaving section is composed of a longitudinal cleavingsection which is substantially linear and a pair of V-shaped lateralcleaving sections ramified and connected respectively both ends in thelongitudinal direction of the longitudinal cleaving section and openingforward and extending obliquely with respect to the direction ofextension of the longitudinal cleaving section.

In the embodiment described above, because the V-shaped lateral cleavingsections opening forward and extending obliquely with respect to thedirection of extension of the longitudinal cleaving section which issubstantially linear, are ramified and connected respectively to bothends in the longitudinal direction of the longitudinal cleaving section,the cleavage of the longitudinal cleaving section which has proceededalong with the inflation of the air bag is ramified smoothly from theends thereof in the longitudinal direction and shifts to the lateralcleaving sections. Accordingly, the cleaving performance duringdeploying the air bag may be improved considerably without particularlythinning the thickness of the cleaving sections. Therefore, it ispossible to obtain the predetermined cleaving performance while keepingthe thickness of the cleaving section to a degree permitting the qualityof appearance to be maintained. This kind of arrangement is effective,in particular in an instrument panel with a skin member having thesingle-layer structure.

In the arrangement described above, a thin portion may be formed bycreating the groove with a certain width at each ramified portion of thecleaving section and the thin portion may be formed into a substantiallytriangular shape that is inversely tapered toward the center of theramified portion from each of the lateral and longitudinal cleavingsections.

In this case, the triangular thin portion provides a certain clearanceor play, so that it is possible to reduce resistance 40 the cleavageramifying to the lateral cleaving section and changing the directionthereof and to ramify the direction of the cleavage, which otherwiseshould advance straight, smoothly from the longitudinal cleaving sectionto the lateral cleaving sections. Thereby, the cleaving performance maybe improved further.

Further, an initial cleaving section may be created substantially at thecenter in the longitudinal direction of the longitudinal cleavingsection by creating the groove with a certain widened width.

It smoothes the initial cleavage of the cleaving section when the airbag inflates and allows the cleaving performance to be improved further.

Still further, the skin member, a door member and a cushion layer may beformed as one body by injecting and foaming a foam material between theskin member, and the door member which is disposed so as to face to theskin member and is pushed open as the air bag inflates, and projections,which break through the cleaving section of the skin member as the airbag inflates, may be provided so as to project from the side of the doormember facing toward the cleaving section to the side of the skinmember.

In this case, the door member is pushed open at first as the air baginflates and the projections, created on the door member, break throughthe cleaving sections of the skin member. Therefore, even if the skinmember is made of a material such as PVC or TPO, which excel inextensibility and flexibility, the skin may be cleaved adequately andreadily along the cleaving sections while keeping the thickness of thecleaving sections created on the skin member to a degree not degradingthe moldability and the durability of the product, i.e., to a degree ofmaintaining the quality appearance of the instrument panel. Thus, thecleaving performance thereof may be improved considerably.

Furthermore, alone the length of the projections, projection portions atthe part facing to the initial cleaving section, or at the parts facingboth of the initial cleaving section and the triangular thin portionsmay be formed higher than projection portions at the part facing otherparts of the cleaving section.

In this case, the higher projection portions break through the initialcleaving section and the triangular thin portions first and the cleavingperformance along the whole cleaving sections thereafter is enhancedfurther.

An instrument panel for an air bag of the present invention comprises askin member, which has at least a cushion layer made of foam resindisposed on the back of a skin layer, and in which a brittle section,which does not reach the skin layer, is created at the partcorresponding to an air bag deployment section; and a door member, madeof synthetic resin, in which a brittle section is created at the partcorresponding to the air bag deployment section by thinning the doormember; and where the skin member is formed as one body with the doormember so that the respective brittle sections face to each other byinjection-molding the synthetic resin on the back of the skin member.

According to the arrangement described above, the door member having thebrittle section is created by injection-molding the synthetic resin onthe back of the skin member having a brittle section so as toconsolidate the skin member and the door member so that those brittlesections face toward each other. The cleaving section which cleaves asthe air bag inflates is created by both brittle sections. Because thecleaving section is not created by cutting the skin member and the doormember after consolidating them, the brittle section of the door memberis not disconnected. That is, the brittle section of the door member isthinned and the whole door member is continuous even though the brittlesection exists, so that the rigidity of the part which turns out to bethe cleaving section when deploying the air bag is enhanced. Therefore,it is possible to suppress stress from concentrating on the brittlesection of the skin member by force applied to the instrument panelduring normal use prevent, the skin layer from being dented or wrinkledlocally and the quality of appearance from dropping. Accordingly, it ispossible to concentrate stress on both the brittle section of the doormember and the brittle section of the skin member facing thereto and tofully enable the predetermined cleaving performance and the air bagdeployment performance when the air bag inflates. Further, unlike in theprior art described above, because the cleaving section is not createdby cutting the door member by means of ultrasonic or high-frequencyafter molding the skin member as one body with the door member, nopost-processing which would be cumbersome and require a highly advancedtechnique in controlling thickness is necessary, so that the productioncost of the whole instrument panel may be reduced.

In the arrangement described above, it is desirable to form the brittlesection of the skin member by a linear or slit cut line having a depthnot reaching the skin layer, enhancing the rigidity of the part of thebrittle section of the skin member corresponding to the cleaving sectionfurther and maintaining the quality of appearance during normal use.

When the linear or slit cut line is created obliquely with respect tothe direction of thickness of the instrument panel, it is possible toprevent resin from infiltrating the inside of the cut line created onthe skin member and the function of the brittle section itself frombeing damaged during inject-molding by setting the inclination of thecut line in direction in which the injected resin will not flow into thecut line.

An instrument panel for an air bag comprises a skin member having atleast a cushion layer made of foam resin and disposed on the back of askin layer and a door member made of synthetic resin in which a brittlesection is created at the part corresponding to an air bag deploymentsection by thinning the door The skin member is formed as one body withthe door member by injection-molding the synthetic resin on the back ofthe skin member so the one body has a uniform thickness over the wholerange. The thickness of a portion of the door member at The brittlesection is thinner than the thickness of the remaining portion and thethickness of a portion of the skin member facing toward the portion ofthe door member adjacent to the brittle section is thicker than that ofthe remaining portion.

According to the arrangement described above, the cleaving performanceand the air bag deployment performance may be enhanced by causing stressto concentrate on the brittle section of the door member when the airbag inflates due to the difference between the thickness of a portion ofthe door member at the brittle section and that of the other portionbecause the thickness of a portion of the door member at to the brittlesection is set to be thinner than that of the other portion whileforming the whole area of the instrument panel generally in a uniformthickness. Further, the rigidity of the part which works as the cleavingsection when the air bag is deployed may be increased and the quality ofappearance may be prevented from dropping because the brittle section ofthe door member is just thinned and the whole door member is continuous.Still more, because the cleaving section is not created by cutting thedoor member, after consolidating the skin member and the door member, bymeans of ultrasonic or high-frequency, a no cumbersome post-processingwhich would require highly a advanced technique in controlling thethickness is necessary and the production cost of the whole instrumentpanel may be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal section view of an instrument panel for an airbag according to a first embodiment of the present invention;

FIG. 2 is a plan view showing a cleaving section of a skin member of theinstrument panel;

FIG. 3 is an enlarged view of a ramified portion of the cleavingsection;

FIG. 4 is an enlarged section view of a groove of the skin member;

FIG. 5 is an enlarged section view showing another example of thegroove;

FIG. 6 is a plan view showing another example of a projection of a doormember in the first embodiment;

FIG. 7 is a plan view showing a still another example of a projection ofthe door member in the first embodiment;

FIG. 8 is an enlarged section view of a main part along lines X--X andY--Y in FIG. 7;

FIG. 9 is an enlarged view of a main part along a line Z--Z in FIG. 7;

FIG. 10 is a longitudinal section view of an instrument panel for an airbag according to a second embodiment of the present invention;

FIG. 11 is an enlarged longitudinal section view showing a main part inFIG. 10;

FIG. 12 is an enlarged longitudinal section view of a main part showinganother example of a cut line of a skin member of the second embodiment;

FIG. 13 is a longitudinal section view of a main part of an instrumentpanel for an air bag according to a third embodiment of the presentinvention; and

FIG. 14 is a longitudinal section view of a main part of a prior artinstrument panel for an air bag.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained belowwith reference to the appended drawings.

FIG. 1 is a section view of an instrument panel for an air bag accordingto a first embodiment of the present invention, wherein the instrumentpanel 10 contains an air bag system 12 for a passenger seat thereunderand serves as a cover for an upper opening of an air bag case 12a.

The instrument panel 10 of the first embodiment is structured by forminga skin member 14 having a single-layer structure, a door member 16 and acushion layer 18 formed as one body by injecting and foaming apolyurethane resin material between the skin member 14 and the doormember 16. That is, the instrument panel 10 is structured by disposingcore members 20, having an opening 20a corresponding to an opening ofthe air bag case 12a, and a pair of door members 16, of a double-leafdoor whose ends are fixed to the core members 20 respectively and whichare made of a resin plate or a metal plate so as to face each other, onthe back of the skin member 14, made of PVC or TPO, and by molding thecushion layer 18, made of semi-hard polyurethane foam, by injecting thepolyurethane resin material between the skin member 14 and the coremember 20 as well as the door member 16.

Referring to FIGS. 2-4, in the instrument panel 10, a cleaving section22 that cleaves as the air bag inflates is formed by a groove 24provided on the back of the skin member 14. The cleaving section 22 isformed as a double-Y shape when seen in plan as shown in FIG. 2. Thatis, the cleaving section 22 is composed of a longitudinal cleavingsection 26, which is formed substantially linearly, and a pair ofV-shaped lateral cleaving sections 28 ramified from both ends in thelongitudinal direction of the longitudinal cleaving section 26 andopening and extending to, right and left with respect to an imaginaryextension line L of the longitudinal cleaving section 26 at an angle Ain a range of about 30°, to 60°, or preferably 45°.

The groove 24 is widened 40 a certain width at each ramified portion ofthe above-mentioned cleaving sections 26 and 28 to create thin portions32 form as bottom walls 24a thereof. The thin portion 32 is formed intoa substantially triangular shape inversely tapered off from each of thelongitudinal and lateral cleaving sections 26 and 28 to the center ofthe ramified portion 30.

Each end 28a of the lateral cleaving section 28 is created so as to beramified again forming semicircular arcs as shown in FIG. 2 to stop theadvancement of cleavage at this portion. It is noted that thesemicircular end 28a may be omitted.

Preferably, the breadth of the triangular thin portion 32 is such thatthe diameter of a circle 34 inscribing the thin portion 32 is about 10to 15 mm as shown in FIG. 3. It is noted that the reference numeral 24bin the figure denotes side walls of the groove 24.

As shown in FIG. 2, there is created an initial cleaving section 36where the groove 24, whose bottom wall 24a normally has a width of 1 mm,is widened to about 3 to 5 mm at the center part of the longitudinalcleaving section 26.

The ends of the door members 16 of the double-leaf door facing towardeach other abut each other under the longitudinal cleaving section 26 asshown in FIG. 1. Projections 38 are provided upwardly at a region facingto the initial cleaving section 36 so as to cleave the initial cleavingsection 36 at first by the projections 38 when the air bag inflates.

It is noted that an open edge angle B of the groove 24 forming thecleaving section 22 is preferred to be in a range of 90° to 60° as shownin FIG. 4 in order to improve the moldability and the initialcleavability.

In the instrument panel 10 of the present embodiment, the door member 16is pushed open at first when the air bag inflates and thereby, theprojections 38 of the door member 16 break through the initial cleavingsection 36.

While the whole longitudinal cleaving section 26 cleaves and thecleavage shifts to the lateral cleaving sections 28, the cleavage of thelongitudinal cleaving section 26 is smoothly ramified and is transmittedto the lateral cleaving sections 28 because the lateral cleavingsections 28 are formed into the shape of a V and diverge at thepredetermined angle A with respect to the direction of extension of thelongitudinal cleaving section 26.

Further, because the substantially triangular thin portion 32 having acertain width is created at the ramified portion 30, it is possible toreduce resistance 40 the cleavage ramifying from the longitudinalcleaving section 26 to the lateral cleaving sections 28 by changing thedirection thereof and to ramify the direction of cleavage, which shouldotherwise advance straight, from the longitudinal cleaving section 26 tothe lateral cleaving sections 28 smoothly.

It is also possible to smoothly conduct the initial cleavage of thewhole cleaving section by creating the initial cleaving section 36 atthe center of the longitudinal cleaving section 26 and by cleaving it bythe projections 38 of the door member 16 and to improve the moldabilityand the initial cleavability of the cleaving sections 26 and 28 byreducing the open edge angle B of the groove 24.

FIG. 5 shows a modified example concerning the shape of the groove 24.The groove 24 has an inverse narrow V shape in this case. By thusreducing the open edge angle B of the groove 24, it is possible tomaintain an advantageous quality of appearance without causing any localdents or uneveness on the gloss of the surface of the skin member 14 andat the same time it is possible to improve the cleavability of the panelduring inflating the air bag by combining this feature with thelongitudinal cleaving section 26 and the substantially Y-letter shapedlateral cleaving sections 28 ramified from and connected at both ends ofthe longitudinal cleaving section 26.

FIG. 6 shows a modified example concerning the projection 38 which isprovided so as to project from the door member 16 to the skin member 14.In this case, the projections 38 are provided so as to project towardthe skin member 14 at the region of the door member 16 facing toward thewhole range of the longitudinal cleaving section 26 and the lateralcleaving sections 28. That is, the projections 38 which face toward thewhole cleaving section 22 are formed by a substantially linearlongitudinal projection 40 which faces toward the longitudinal cleavingsection 26 and a pair of lateral projections 42, ramified from both endsin the longitudinal direction of the longitudinal projection 40 andopening and extending in the shape of "V" to the to right and left at anangle A in a range of about 30° to 60° with respect to the extensionline L of the longitudinal projection 40.

When the projections 38, which face the whole range of the cleavingsection 22, are provided by the substantially linear longitudinalprojection 40 and the pair of V-shaped lateral projections 42 linkedwith both ends of the longitudinal projection as described above, thecleavage advances as the longitudinal projection 40 and the lateralprojections 42 created on the door member 16 break through the brittlepart of the skin member 14 forming the longitudinal cleaving section 26and the lateral cleaving sections 28, respectively, when the door member16 is pushed open by the inflation of the air bag. Accordingly, it ispossible to suppress and minimize small pieces of urethane from flyingdue to the deviation of the locus of cleavage and to the rupture of thecushion layer 18 by fully effecting the adequate cleavability along thecleaving section 22 while relatively increasing the thickness of thecleaving section 22 created on the skin member 14 to a degree notdegrading the moldability thereof and the durability of the product whenthe skin member 14 is made of a material excellent in extendibility andflexibility such as PVC and TPO.

FIG. 7 shows a still further example concerning the projections 38provided so as to project from the door member 16 toward the skin member14. In the arrangement in which the projections 38 are provided over thewhole range of the cleaving section 22 as shown in the example in FIG.6, the shape of the projection 38 is modified as described below. Thatis, a height H, which is a length of the projection from the upper faceof the door member 16, as shown in FIG. 8, of a projection 38a at thepart facing to the initial cleaving section 36 and of a projection 38bat the part facing to the substantially triangular thin portion 32 isincreased more than a height h (shown in FIG. 9) of the projection 38facing other parts of the cleaving section 22 as shown in FIG. 7. Of theentire length of the projections 38 created on the door member 16 whichare pushed open due to the inflation of the air bag, the projections 38aand 38b whose height is higher break through the initial cleavingsection 36 and the substantially triangular thin portion 32 first andthe cleavage further along the whole cleaving section 22 which thentakes place thereafter is enhanced, by adopting such an arrangement.

FIG. 10 is a longitudinal section view of the main part of an instrumentpanel for an air bag according to a second embodiment of the presentinvention. Similar to the first embodiment, the instrument panel 50contains the air bag system 12 for the passenger seat and covers theupper opening of the air bag case 12a.

The instrument panel 50 of the second embodiment is structured byforming a skin member 52, having a double-layer structure, as one bodywith a door member 54 by inject-molding thermoplastic resin forming thedoor member 54 on the back of the skin member 52. The instrument panel50 has a cleaving section 56 having a double Y-letter shape or anH-letter shape when seen in plan view at the parts corresponding to theair bag deployment section of the first embodiment. The edge portion ofthe door member 54 is fixed to the core member 20.

The skin member 52 comprises three layers, a skin layer 58 molded usingpolyolefine resin such as PP (polypropylene) or PVC, a cushion layer 60formed by polyolefine foam such as PP foam on the back of the skin layer58 and a barrier layer 62 made of soft resin, which three layers areattached to each other to form a body as shown in FIG. 11. A brittlesection 64, formed as a linear or slit cut line having a depth notreaching the skin layer 58 but existing at the barrier layer 62 andreaching the lower half of the cushion layer 60, is created on the backof the skin member 52 at the part corresponding to the air bagdeployment section.

The linear or slit cut line, which is the brittle section 64 on the sideof the skin member 52, may be created (1) by inserting ultrasonic waveor high frequency laser to the depth reaching to the barrier layer 62and the lower half of the cushion layer 60 after molding the skin layer58, the cushion layer 60 and the barrier layer 62 attached to each otherin a body, or (2) by molding the skin layer 58 and the cushion layer 60in a body in advance, and on its back disposing and adhering the barrierlayer 62 in which the linear or slit cut line has been created.

The door member 54 is adhered on the back of the skin member 52 as onebody with it by setting the skin member 52 on a mold not shown and byinjection-molding relatively hard thermoplastic material such asdenaturation PP. thin brittle section 68 is created by providing agrooved portion 66 dented toward the skin member 52, at the partcorresponding to the air bag deployment section, i.e., at the partfacing to the brittle section 64 of the skin member 52.

Because the instrument panel 50 is structured by creating the brittlesections 64 and 68 in the skin member 52 and the door member 54respectively, and the cleaving section 56 is provided by both brittlesections 64 and 68 by forming both members 52 and 54 in one body, itbecomes totally unnecessary to implement the post-processing creatingthe cleaving section by cutting it by ultrasonic or high-frequency aftermolding both members 52 and 54 in a body which would be cumbersome andrequire highly a advanced technique in controlling the thickness.Further, the injection-molding means may be readily adopted in moldingthe door member 54, so that the production cost of the whole instrumentpanel 50 may be reduced. Further, because the brittle section 68 of thedoor member 54 is thin and the whole door member 54 is one continuousmember having no disconnection, the rigidity around the cleaving section56 may be enhanced. Therefore, even if force is applied to theinstrument panel 50 by touching by a hand, for example, during normaluse, stress is not concentrated on the brittle section 64 of the skinmember 52, and the skin layer 58 will not dent or wrinkle locally andthe quality of appearance does not drop. Nevertheless, when the air bagis actuated and inflated, stress is concentrated on the thin brittlesection 68 of the door member 54, thus rupturing it. Stress is thenconcentrated on the brittle section 64 of the skin member 52 by theruptured door member 54, and the skin member 52 is cleaved along thecleaving section 56 while being adhered and fixed to the door member 54and the air bag may be deployed in a prescribed manner.

It is noted that because the brittle section 64 of the skin member 52 iscreated by the linear or slit cut line at a depth not reaching the skinlayer 58 in the case of the second embodiment, the rigidity and thequality of appearance of the instrument panel 50 may be well maintainedduring normal use i.e., during the time when the air bag is notinflated.

Considering in particular that the door member 54 is a member molded byinjection-molding, it is possible to prevent resin from infiltratinginto the brittle section 64 created in the skin member 52 by setting thedirection of inclination of the cut line in the direction such that theresin to be injected will not flow into the cut line as shown in FIG.12.

FIG. 13 is a longitudinal section view of a main part of an instrumentpanel for an air bag according to a third embodiment of the presentinvention. According to the present embodiment, the skin member 52 andthe door member 54, in which the brittle section 68 is created bythinning the door member 54, are molded as one body by injection-moldingthe resin material of the door member to a uniform the thickness T overthe whole range of the instrument panel and to render the thickness T1of a portion 54a of the door member 54 adjacent to the brittle section68 to be set thinner than the thickness T2 of the other portion 54b,i.e., T2=2T1 to 3T1, in the arrangement of the second embodiment. Inother words, the thickness t1 of a portion 62a of the barrier layer 62of the skin member 52 corresponding to the portion 54a of the doormember 54 adjacent to the brittle section 68 is set to be thicker thanthe thickness t2 of the other portion 62b of the barrier layer 62 byabout 2 to 3 times.

It is noted that an area M in the horizontal direction of the portion54a adjacent to the brittle section 68 where the thickness T1 is thinnerthan the thickness T2 of the other portion 54b corresponds to an areawhich connects portions around both hinge points of the door member 54when it cleaves along the inflation of the air bag.

Although no brittle section 64 of the skin member 52 is shown in thethird embodiment, such a brittle section 64 may be created. The otherfeatures are the same as those in the second embodiment, the samereference numerals refer to the corresponding parts and theirexplanation is be omitted here.

Similar to the second embodiment, in the third embodiment it is totallyunnecessary to implement the cumbersome post-processing of creating thecleaving section by cutting it by ultrasonic or high-frequency after theproduction, which would require a highly advanced technique incontrolling the thickness. Further, the injection-molding means may bereadily adopted in molding the door member 54, so that the productioncost of the whole instrument panel 70 may be reduced. Further, it ispossible to enhance the rigidity of the cleaving section 56 and toprevent the quality of appearance from dropping by forming the wholedoor member 54 as one continuous member. Still more, it is possible toenhance the air bag deployment performance by concentrating stress onthe brittle section 68 of the door member 54 to cleave the panel at thebrittle section 68 by differentiating the thickness of the portion 54aof the door member 54 adjacent to the brittle section 68 from that ofthe other portion 54b and the thickness of the barrier layer portion 62aof the skin member 52 corresponding to the portion 54a of the doormember 54 adjacent to the brittle section 68 from that of the otherbarrier layer portion 62b.

It is noted that although the skin member 52 has the three-layerstructure in the second and third embodiments described above, it mayhave a two-layer structure without having the barrier layer 62. However,the depth of the brittle section 64 must be within the range of thethickness of the cushion layer 60.

As described above, according to the inventions described, the V-shapedvertical cleaving sections, opening forward and extending obliquely withrespect to the direction of extension of the substantially linearlongitudinal cleaving section, are ramified respectively from both endsin the longitudinal direction of the longitudinal cleaving sectioncreated by a groove provided on the back of a skin member, so thatcleavage of the longitudinal cleaving section, which has proceeded alongwith the inflation of the air bag, is ramified smoothly from the ends inthe longitudinal direction to the lateral cleaving sections.Accordingly, the cleaving performance when deploying the air bag may beimproved considerably without particularly thinning the thickness of thecleaving sections and thereby, it is possible to reconcile the cleavingperformance and the quality of appearance.

According to the inventions described, in no post-processing of cuttingthe brittle section by ultrasonic or high-frequency after molding theskin member in a body with the door member, which would be cumbersomeand require a highly advanced technique in controlling the thickness, isnecessary, so that the production cost of the whole instrument panel maybe reduced, and the whole panel may be formed as one continuous panelwithout disconnecting the base material a and the rigidity of the partcorresponding to the cleaving section may be increased. Thereby, it ispossible to suppress stress from concentrating on the brittle section ofthe skin member by force applied to the instrument panel during normaluse, and prevent the skin layer from being dented or wrinkled locallyand the quality of appearance from dropping. Nevertheless, it ispossible to concentrate stress on the brittle section of the door memberand the brittle section of the skin member facing thereto and to fullyeffect the predetermined cleaving performance and the air bag deploymentperformance when the air bag inflates.

According to the invention, in addition to that no post-processing ofcutting the cleaving section by ultrasonic or high-frequency after themolding which would be cumbersome and require highly a advancedtechnique in controlling the thickness is necessary, the production costof the whole instrument panel may be reduced, the rigidity of the partwhich turns out to be the cleaving section when the air bag is deployedis increased and the quality of appearance is prevented from dropping,the cleaving performance and the air bag deployment performance isenhanced by causing stress to concentrate on the brittle section of thedoor member when the air bag inflates by differentiating the thicknessof a portion of the door member adjacent to the brittle section fromthat of the other portion.

What is claimed is:
 1. An instrument panel for use with an air bag whichcleaves to permit deployment of the air bag, the instrument panelcomprising:a skin member having an front surface and a back surfaceopposite said front surface, and said skin member having a cleavingsection defined on said back surface which cleaves apart as the air baginflates and applies pressure to said back surface, said cleavingsection including:a longitudinal cleaving section which is asubstantially linear groove, defined by said back surface, havinginclined groove side surfaces opposing one another, a substantially flatplanar groove bottom surface extending between said groove sidesurfaces, and first and second ends; and first and second V-shapedlateral cleaving sections which are branching grooves, defined by saidback surface, each having inclined branch groove side surfaces opposingone another, a substantially flat planar branch groove bottom surfaceextending between said groove side surfaces, contiguous with andramified respectively from said first and second ends extendingobliquely with respect to virtual longitudinal extensions of saidlongitudinal cleaving section extending in a longitudinal direction ofsaid longitudinal cleaving section.
 2. The instrument panel for an airbag according to claim 1, wherein said cleaving section includes saidsubstantially flat planar groove bottom surface and said substantiallyflat planar branch groove bottom surfaces forming a ramified bottomportion centered about each of said first and second ends and whereatsaid substantially flat planar groove bottom surface and saidsubstantially flat planar branch groove bottom surfaces are wider thanat adjacent portions thereof to form a substantially triangular shapewith sides inversely tapered toward a center of said ramified bottomportion.
 3. The instrument panel for an air bag according to claim 1 or2, wherein said cleaving section includes an initial cleaving sectionsubstantially at a longitudinal center thereof whereat saidsubstantially flat planar groove bottom surface is wider than atadjacent portions of said substantially flat planar groove bottomsurface outside of said initial cleaving section.
 4. The instrumentpanel for an air bag according to any one of claims 1 or 2, furthercomprising:a door member; a cushion layer formed between said doormember and said skin member to form one body by injecting and foaming afoam material between said skin member and said door member which isdisposed so as to face toward said skin member and open as the air baginflates; and said door member having a projection projecting toward thecleaving section of said skin member so as to effect cleaving of saidcleaving section as said air bag inflates and pushes said door open. 5.An instrument panel for use with an air bag which cleaves to permitdeployment of the air bag, the instrument panel comprising:a skin memberhaving an front surface and a back surface opposite said front surface;said skin member having a cleaving section defined on said back surfacewhich cleaves apart as the air bag inflates and applies pressure to saidback surface, said cleaving section including:a longitudinal cleavingsection which is a substantially linear groove, defined by said backsurface, having first and second ends; and first and second V-shapedlateral cleaving sections which are branching grooves, defined by saidback surface, each contiguous with and ramified respectively from saidfirst and second ends extending obliquely with respect to virtuallongitudinal extensions of said longitudinal cleaving section extendingin a longitudinal direction of said longitudinal cleaving section; adoor member; a cushion layer formed between said door member and saidskin member to form one body by injecting and foaming a foam materialbetween said skin member and said door member which is disposed so as toface toward said skin member and open as the air bag inflates; said doormember having a projection projecting toward the cleaving section ofsaid skin member so as to effect cleaving of said cleaving section assaid air bag inflates and pushes said door open; said substantiallylinear groove including an initial cleaving section substantially at alongitudinal center thereof whereat said substantially linear groove iswider than at adjacent portions of said substantially linear grooveoutside of said initial cleaving section; and said projection having atleast one initial cleaving projection portion projecting toward saidinitial cleaving section having a height higher than a remainder of saidprojection to project closer to said cleaving section than saidremainder of said projection.
 6. The instrument panel for an air bagaccording to claim 5, wherein:said substantially linear groove hasinclined groove side surfaces opposing one another, a substantially flatplanar groove bottom surface extending between said groove sidesurfaces; and said branching grooves each have inclined branch grooveside surfaces opposing one another, a substantially flat planar branchgroove bottom surface extending between said groove side surfaces. 7.The instrument panel for an air bag according to claim 6, wherein saidcleaving section includes said substantially flat planar groove bottomsurface and said substantially flat planar branch groove bottom surfacesforming a ramified bottom portion centered about each of said first andsecond ends and whereat said substantially flat planar groove bottomsurface and said substantially flat planar branch groove bottom surfacesare wider than at adjacent portions thereof to form a substantiallytriangular shape with sides inversely tapered toward a center of saidramified bottom portion.
 8. The instrument panel for an air bagaccording to claim 7, wherein said projection includes at least a secondinitial cleaving projection portion projecting toward at least and saidramified bottom portion having a height higher than a reminder of saidprojection, excluding said at least one initial cleaving projection, toproject closer to said cleaving section than said remainder of saidprojection.
 9. An instrument panel for use with an air bag which cleavesto permit deployment of the air bag, the instrument panel comprising:askin member having a front skin member surface and a back skin membersurface, said skin member including a skin layer having a front surface,forming said front skin member surface, and a back surface and at leasta cushion layer made of foam resin and disposed on the back surface ofsaid skin layer; said skin member having a frangible skin section formedin at least said cushion layer, but not in said skin layer, at a partcorresponding to an air bag deployment section; a door member, made ofsynthetic resin, having a frangible door section at a positioncorresponding to said air bag deployment section which is formed by aportion of said door member which is thinner than adjacent portions ofsaid door member; and said skin member being formed as one body withsaid door member by injection-molding said synthetic resin on said backskin member surface so that said frangible skin section and saidfrangible door section face each other.
 10. The instrument panel for anair bag according to claim 9, wherein said frangible skin section ofsaid skin member is formed by a cut in said cushion layer having a depthnot reaching said skin layer.
 11. The instrument panel for an air bagaccording to claim 10, wherein said cut is disposed obliquely withrespect to said back skin member surface.
 12. An instrument panel for anair bag, comprising:a skin member having a front skin member surface anda back skin member surface, said skin member including a skin layerhaving a front surface, forming said front skin member surface, and aback surface and at least a cushion layer made of foam resin anddisposed on the back surface of said skin layer; a door member made ofsynthetic resin, having a frangible door section at a positioncorresponding to said air bag deployment section; said skin member beingformed as one body with said door member by injection-molding saidsynthetic resin of said door member on the back skin member surface ofsaid skin member so said one body has a uniform thicknes; said doormember having a thin door portion, including said frangible doorsection, which is thinner than adjacent portions of said door member andsaid skin member having a thick skin member portion, facing said thindoor portion, that is thicker than adjacent portions of said skinmember.
 13. An instrument panel for use with an air bag which cleaves topermit deployment of the air bag, the instrument panel comprising:a skinmember having an front surface and a back surface opposite said frontsurface; said skin member having a cleaving section defined on said backsurface which cleaves apart as the air bag inflates and applies pressureto said back surface, said cleaving section including:a longitudinalcleaving section which is a substantially linear groove, defined by saidback surface and having first and second ends; and first and secondV-shaped lateral cleaving sections which are branching grooves, definedby said back surface, contiguous with and ramified respectively fromsaid first and second ends extending obliquely with respect to virtuallongitudinal extensions of said longitudinal cleaving section extendingin a longitudinal direction of said longitudinal cleaving section; andsaid cleaving section including said substantially linear groove andsaid branching grooves forming a ramified portion centered about each ofsaid first and second ends and whereat said substantially linear grooveand said branching grooves are wider than at adjacent portions thereofto form a substantially triangular shape with sides inversely taperedtoward a center of said ramified portion.
 14. The instrument panel foran air bag according claim 13 wherein said cleaving section includes aninitial cleaving section substantially at a longitudinal center thereofwhereat said substantially linear groove is wider than at adjacentportions of said substantially linear groove outside of said initialcleaving section.
 15. An instrument panel for use with an air bag whichcleaves to permit deployment of the air bag, the instrument panelcomprising:a skin member having an front surface and a back surfaceopposite said front surface; said skin member having a cleaving sectiondefined on said back surface which cleaves apart as the air bag inflatesand applies pressure to said back surface, said cleaving sectionincluding:a longitudinal cleaving section which is a substantiallylinear groove, defined by said back surface and having first and secondends; and first and second V-shaped lateral cleaving sections which arebranching grooves, defined by said back surface, contiguous with andramified respectively from said first and second ends extendingobliquely with respect to virtual longitudinal extensions of saidlongitudinal cleaving section extending in a longitudinal direction ofsaid longitudinal cleaving section; and said cleaving section includingan initial cleaving section substantially at a longitudinal centerthereof whereat said substantially linear groove is wider than atadjacent portions of said substantially linear groove outside of saidinitial cleaving section.